Forests

The forest land area of North America increased from an estimated 719 million hectares (ha) in 2005 to more than 723 million ha in 2015 and now represents 36% of the land area in North America and 18% of the world’s forest land area (FAO 2016b). The increase in forest land area over the last decade was driven entirely by gains in the United States, while Canada and Mexico both lost forestland (see Table 9.1). The area of other wooded lands also increased in North America over the last decade, with substantial gains in the United States, no change in Canada, and loss in Mexico.

Forest ecosystems are the largest terrestrial carbon sink on Earth, and their management has been recognized as a relatively cost-effective strategy for offsetting greenhouse gas (GHG) emissions (Canadell and Schulze 2014). In North America, forests—including urban forests, woodlands, and the products obtained from them—play a major role in the carbon cycle (Goodale et al., 2002). Since this report includes forestland from Canada, Mexico, and the United States, forestland is defined according to the Global Forest Resource Assessments from the United Nations Food and Agricultural Organization (FAO 2010, 2016b). This definition also is widely used for land representation in GHG reporting to the United Nations Framework Convention on Climate Change (UNFCCC; see U.S. EPA 2018) to ensure consistency and comparability in national reporting. Forest area is defined as land spanning greater than 0.5 ha with trees higher than 5 m and canopy cover of more than 10%, or trees able to reach these thresholds in situ. Other wooded lands are defined as land not classified as forest, spanning greater than 0.5 ha with 1) trees higher than 5 m and a canopy cover of 5% to 10%; 2) trees able to reach these thresholds in situ; or 3) land with a combined cover of shrubs, bushes, and trees above 10%. Forests and other wooded land do not include land predominantly used for agriculture or urban purposes (FAO 2010). For this reason, urban forests are not included in this chapter, but their contribution to total carbon stocks and stock changes is described.

Forests’ capacity to uptake and store carbon is influenced by many socioeconomic and biophysical factors (Caspersen et al., 2000; Joos et al., 2002; Birdsey et al., 2006; Zhang et al., 2012). Sustained investment in afforestation, reforestation, and improved forest management is an option for elevating the role forests play in future climate mitigation. This chapter presents the most recent estimates of carbon stocks and stock changes across the continuum of land with trees in North America and highlights advances in forest carbon cycle science since the First State of the Carbon Cycle Report (SOCCR1; CCSP 2007).